The invention herein relates to bubble-blood oxygenators of the type used in thoracic surgery, and more particularly to an improved means for directing the flow of blood and blood foam onto the heat exchanger of such oxygenators. The present invention is an improvement upon and useful in connection with the devices shown in Bentley U.S. Pat. No. 4,282,180 issued Aug. 4, 1981, entitled "Blood Oxygenator".
The history of safe and reliable blood oxygenators is relatively brief. Such oxygenators are used in open-heart surgery and other operations and treatments of the body when it is necessary to establish an extracorporeal circulation system for temporarily assuming the function of the heart and lungs of the patient. In such a system, the oxygenator operates to perform the function usually performed by the lungs of the patient, i.e. the life supporting transfer of oxygen into the blood and the carbon dioxide out of the blood. In addition to gas transfer, the oxygenator serves to cool or heat the extracorporeal blood. Cooling the blood cools the patient which resultantly reduces the oxygen requirements of the patient. Since less oxygenation is required, the volume of extracorporeal blood needed to be oxygenated is less.
Oxygenators which both oxygenate the blood and regulate its temperature have been well known. Such oxygenators of the bubble-blood type operate by mixing oxygen deficient, i.e. venous, blood with oxygen to produce blood foam. The blood and blood foam is then flowed over a heat exchanger element and into a defoaming stage where the oxygenated, temperature regulated blood is stored for use in the patient.
The mixing of the venous blood with the oxygen will typically occur in some form of mixing chamber. For example, in an early bubble blood oxygenator containing an integral heat exchanger, designed by Dr. Frank Gollan in the 1950's and published in his book The Physiology of Cardiac Surgery, Hypothermia, Extracorporeal Circulation and Extracorporeal Cooling, the blood foam is produced by forcing oxygen through a sparger plate of sintered glass into the lower portion of the bubble column into which the venous blood is introduced. The blood foam then flows up the bubble column, over the heat exchanger section and into a defoamer section. No attempt was made to preferentially direct the blood foam onto the heat exchanger section.
Currently available bubble blood oxygenators do not specifically attempt to direct the flow of blood foam onto the heat exchanger section. The blood oxygenator described in Bentley U.S. Pat. No. 4,282,180 utilizes a blood-oxygen mixing area and an integral heat exchanger. Considering in more detail the blood-oxygen mixing area of the oxygenator described in Bentley U.S. Pat. No. 4,282,180, incorporated herein by reference, as schematically shown in FIG. 1, the venous blood is introduced into an annular chamber 14 in a generally tangential manner. As the blood circles in the annular chamber 14, oxygen gas is introduced in bubble form into the chamber through a diffusion means 13 in the chamber bottom. The blood and oxygen bubbles form blood foam which passes from the annular chamber through a distribution channel 16, over a mixing plate 20, and into a mixing chamber 17 which contains the heat exchanger 18.
The preferred heat exchanger design consists of a helically coiled, ribbed heat exchanger conduit over which the blood and blood foam is flowed. Since the conduit shape is a helical spiral the upper end of the conduit is necessarily closer to the top of the oxygenator than is a portion of the conduit which is further down the helix. Accordingly, the gap between the distribution channel and the heat exchange coil increases as one proceeds down the helix of the conduit. No preferential direction is imparted to the blood foam leaving the distribution channel.
Blood and blood foam have a fairly high degree of surface tension which sometimes causes undirected or unconstrained blood to flow together. As a result, blood and blood foam may occasionally flow over the mixing plate and onto the heat exchange conduit unevenly, more flowing onto one portion of the coil than another.